Enzyme Kinetics: Saturation and Inhibition

Enzyme Kinetics and Inhibition

Enzyme Activity Plateau

  • As conditions (e.g., temperature initially) are optimized, enzyme activity increases.

  • However, a plateau is eventually reached where the reaction rate becomes stationary and no further increase in enzyme activity occurs.

  • This plateau signifies that:

    • All available enzyme active sites are occupied by substrate molecules (enzyme saturation).

    • Essentially, all enzyme has been utilized, or all available substrate has been processed up to the maximum rate possible for the given enzyme concentration.

    • At this point, even if additional enzyme or substrate is introduced, the reaction rate will not increase because the enzyme is working at its maximal capacity or is saturated with substrate.

Reversible Competitive Inhibition

  • Definition: Reversible competitive inhibitors are molecules that resemble the substrate and bind to the enzyme's active site, preventing the actual substrate from binding.

  • Mechanism of Reversibility: This type of inhibition is termed "reversible competitive" because it can be overcome.

    • If the concentration of the substrate is significantly increased, the substrate molecules can outcompete the inhibitor for the active site.

    • This higher substrate concentration effectively "throws the inhibitor off" the active site, allowing the substrate to bind instead.

    • Once the substrate replaces the inhibitor, the enzyme can resume its catalytic activity.

Feedback Inhibition

  • Definition: Feedback inhibition is a regulatory mechanism where the end product of a metabolic pathway acts as an inhibitor for an enzyme earlier in the same pathway.

  • Mechanism: When there is an excess accumulation of the end product:

    • The end product molecule binds to an allosteric site on an enzyme typically located at an early, committed step of its own biosynthetic pathway.

    • This binding alters the enzyme's conformation, reducing or stopping its activity.

    • This mechanism prevents the overproduction of the end product, ensuring cellular resources are not wasted and maintaining metabolic balance.

    • It acts as an internal control system, telling the pathway to slow down or stop when sufficient product is available.